1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copying machine and an electrophotographic printer and a process cartridge detachably mountable to a main body of the image forming apparatus.
Here, an electrophotographic image forming apparatus forms an image on a recording sheet using an electrophotographic image forming method, and examples of the electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (for example, a laser beam printer and an LED printer), a facsimile machine and a word processor.
Further, a process cartridge is a cartridge into which at least one of an electrophotographic photosensitive drum and charging means for charging the electrophotographic photosensitive drum are integrally incorporated, the cartridge being detachably mountable to a main body of an image forming apparatus.
2. Description of the Related Art
Conventionally, as an electrophotographic image forming apparatus, there is a color electrophotographic image forming apparatus of an in-line type in which multiple process cartridges are aligned. There is a contact development method of performing a development in the state in which a developing roller composing a process cartridge is in contact with a photosensitive drum. In this method, in order to keep a predetermined contact pressure between the developing roller and the photosensitive drum during an image formation, the developing roller is urged against the photosensitive drum.
In the case of this method, when the process cartridge is not used for a long time period in the state of being mounted on the main body of the image forming apparatus, there is a possibility that an elastic layer of the developing roller is permanently deformed. Whereby, an uneven image may be formed at the time of development.
Then, proposed is a process cartridge and an image forming apparatus in which there is provided a mechanism for separating a developing roller from a photosensitive drum in the case of performing no image forming operation (Japanese Patent Application Laid-Open No. 2005-172906).
On the other hand, the construction in which a charging roller is brought into contact with a photosensitive drum for charging the photosensitive drum is widely used. In such a contact charging, the charging roller needs to be disposed reliably in contact with the surface of the photosensitive drum, and hence the charging roller is in pressure contact with the surface of the photosensitive drum at a predetermined contact pressure. When the state of not being used for a long time period in this state continues, the elastic layer of the charging roller is permanently deformed, and thus an uneven density of an image of the rotation cycle of the charging roller occurs.
Thus, proposed is a method in which an insert member for separating the charging roller from the photosensitive drum is inserted into therebetween at the time of shipment of a process cartridge, and a user removes the insert member in use (Japanese Patent Application Laid-Open No. H05-188667).
Alternatively, proposed is a process cartridge having a mechanism in which a charging roller having been separated until then is brought into contact with a photosensitive drum when the process cartridge is mounted on the main body of the image forming apparatus (Japanese Patent Application Laid-Open No. H06-273987 and Japanese Patent Application Laid-Open No. 2000-181328).